Fuel Cell Voltage Monitoring Considerations

Voltage Monitor

 

Knowing what’s happening inside a fuel cell is a critical function, especially as fuel cells are continuing to be developed. One important aspect of this is to measure the voltage of each cell in a stack. Although this may sound trivial, it can be more complex and more expensive than it may at first appear due to high voltages, high channel counts, communication types, etc. There are a few products commercially available that are designed specifically for fuel cell voltage monitoring.

 

Table 1 (below) lists some of the Cell Voltage Monitors (CVMs) currently available – there may be a few others available but these represent the most common. One feature that sets CVMs apart from other, more mainstream data acquisition systems is the fact that the signal side is completely isolated and electrically floating relative to the communication and power supply portion of the electronics. This allows high voltage stacks to be measured and the capability of cascading multiple CVMs together to measure the large numbers of cells in high voltage stacks. All of the units listed have this ability.

 

Another important feature in a CVM system is high-speed acquisition. Again, this is especially important in systems with high cell counts since most CVM systems measure each channel in sequence and the larger the stack the longer it takes to measure all the cells. The newly released CVM designed by Lynntech and offered by FuelCellsEtc.com is especially remarkable in acquisition rate, with a rate of up to 5 kHz (4x faster than other systems) – a rate that is maintained regardless of how many CVM modules are linked together. This allows the researcher to closely analyze any voltage anomalies during load transients, regardless of the number of cells being monitored.

 

The third important aspect in measuring fuel cell voltages is accuracy. Accuracy, in conjunction with speed, allow the control system (or the researcher) to better diagnose what is happening inside the fuel cell. Voltage characteristics of the cells can provide information about the humidification of each cell, the health of the catalyst, which cells may be exhibiting crossover, and a myriad of other information important to the operation of the fuel cell. There are a number of ways to ensure accurate voltage measurements. Accuracy begins with noise reduction and equipment selection. The CVM should be placed as close to the fuel cell being tested as possible, minimizing the cable length between the CVM and the fuel cell. This will reduce the amount of noise picked up by the cables and transmitted to the CVM. In addition, the CVM must be selected to provide as much accuracy as possible – It is far easier to filter and smooth a high accuracy signal than it is to try to obtain additional accuracy later.

 

These are the primary drivers of CVM selection, although many other factors may come into play: available communication standards, removable storage options, size, power consumption, etc. Overall, the total cost to implement the solution must be considered. Even if the unit cost may be slightly less for one unit, be aware of what other necessary components would cost, such as cabling, software, LabView drivers, etc. The Lynntech Cell Voltage Monitor includes all software and LabView drivers in the initial price while the cable is designed for a simple, low-cost IDC style connector and ribbon cable (similar to a hard-drive cable), resulting in an overall lowest cost solution even while providing superior performance characteristics than other solutions.

 

Daniel Westerheim is Manager of FuelCellsEtc.com; a supplier of custom fuel cell components supplier including Lynntech MEAs and Cell Voltage Monitor. Visit our store for a list of other products and services or to purchase a CVM . If you would like to ask Daniel a question please email him at AskUs@FuelCellsEtc.com or fill out our Contact Us form.

 

FuelCellsEtcEuroTech (SMART Fuel Cell)EuroTech (SMART Fuel Cell)EuroTech (SMART Fuel Cell)EuroTech (SMART Fuel Cell)FuelConFuelConFuelConYokogawaYokogawa
FuelCellsEtcEuroTech (SMART Fuel Cell)EuroTech (SMART Fuel Cell)EuroTech (SMART Fuel Cell)EuroTech (SMART Fuel Cell)FuelConFuelConFuelConYokogawaYokogawa
ModelCVM 2582ACVM Pro60CVM Pro90Basic S/WGraphic S/WTrue Data - CVM 10True Data - CVM 50True Data - CVM 70DX2040DX2048
Price$1,995.00$7,000.00$8,200.00$1,100.00$3,200.00$3,225.00$10,275.00$7,250.00$7,930.00
Channels3260901050704048
Additional IO2 K-type TC inputs (12-bit) 14 (10-bit) Analog Inputs (Optional) 16 Digital IO (Optional)
CascadingYes (CAN: 16 boards - 512 channels; USB virtual unlimited)Yes (up to 2790 channels)Yes (up to 2790 channels)N/AUp to 10 devices (500 Channels)Up to 10 devices (500 Channels)
Cell ConnectorsIDC2 x Sub-D 25 pin2 x Sub-D 25 pin
InterfaceUSB, CAN, RS232, RS485(2) independent CAN buses (1 data, 1 control)(2) independent CAN buses (1 data, 1 control)Ethernet, CAN, RS232Ethernet, CAN, RS232Ethernet, CAN, RS232USB, RS232, RS422A/485USB, RS232, RS422A/485
AlarmsStatus LEDContact Breaks; Masking of Individual Cells; alarming at violations of thresholdsContact Breaks; Masking of Individual Cells; alarming at violations of thresholdsStatus-LED; Error BeepStatus-LED; Error BeepStatus-LED; Error Beep
WebserverOptionalOptionalOptional
Data MemorymicroSDCompact FlashCompact FlashCompact Flash80MB80MB
Voltage Range+/- 2.0V or 0 to 4.096V+/- 1.2V or +/- 2.8V+/- 1.2V or +/- 2.8V-2.5 VDC to +2.5 VDC-2.5 VDC to +2.5 VDC-2.5 VDC to +2.5 VDC
Resolution16 bit12 bit12 bit12 bit12 bit12 bit
Voltage Accuracy+/- 63 uV0.10%0.10%+/- 1 mV+/- 1 mV+/- 1 mV
Sample Time<0.25 ms/channel (<8 ms / 32 channels)1 ms /channel (cycle time 80ms or 110ms)1 ms /channel (cycle time 80ms or 110ms)< 2 ms / channel< 2 ms / channel< 2 ms / channel
Electrical Separation32 Isolated ChannelsAll Channels isolatedAll Channels isolatedAll Channels isolated
Isolation Voltage1 kV1 kV1 kV1 kV1 kV1 kV
Common Mode Rejection85 VDC80 VDC80 VDC80 VDC
Operation Temperature0 C to 50 C-25 C to +85 C-25 C to +85 C0 C to 35 C0 C to 35 C0 C to 35 C0 C to 50 C0 C to 50 C
Dimensions121 x 104 x 32 mm (4.7" x 4.1" x 1.2")210 x 165 x 85 mm (8.27" x 6.50" x 3.35")210 x 165 x 85 mm (8.27" x 6.50" x 3.35")210 x 165 x 85 mm (8.27" x 6.50" x 3.35")288 x 288 x 221.6 mm288 x 288 x 221.6 mm
Weight0.25 kg (0.55 lb)1.8 kg (3.97 lbs)1.8 kg (3.97 lbs)1.8 kg (3.97 lbs)7.3 kg (16.1 lb)7.3 kg (16.1 lb)
EnclosureIP 54IP 54IP 54IP 54IP 54
Power Consumption<2.5 W (500 mA)35 W35 W35 W
Power SupplyUSB or External +8 to +30 VDC7 to 60 VDC7 to 60 VDC24 VDC (Power Supply Optional)24 VDC (Power Supply Optional)24 VDC (Power Supply Optional)24 VDC24 VDC

 

Comments

  1. S roy choudhury says:

    Can it be for phosphoric acid fuel cells

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